Multi-cavity klystron



March 12, 1957 R. H. DlCKE 2,785,335

MULTI-CAVITY KLYSTRON Filed May 15, 1946 FIG. I

INVENTOR ROBERT H. DICKE ATTORNEY United States Patent MULTI-CAVITY KLYSTRON Robert H. Dicke, Princeton, N. 1., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 15, 1946, Serial No. 669,733

4 Claims. (Cl. SIS-5.39)

This invention relates to klystron tubes and more particularly to an improvement in the cavity structure of klystron tubes.

The conventional two cavity klystron consists of two cavitiescoupled electromagnetically but separated by a drift space, the latter consisting of the space between the cavities. Electrons ejected from a gun traverse both cavities. The first cavity velocity modulates this stream of electrons. The electrons form into bunches in the drift space and then traverse the second cavity in bunches. The magnitude of the velocity modulation introduced by the first cavity is proportional to the radio frequency voltage applied to the first cavity. The energy which a givenelectron bunch gives up to the second cavity is proportional to the number of electrons in the bunch and the voltage in the second cavity, but the power dissipated in the cavities is proportional to the voltage squared. From this it is seen that power extracted from the electron beam is proportional to the cavity voltage, but the sum of the power dissipated in the cavity and external load is proportional to the voltage squared. These two powers must be equal. The limitation in the efiiciency of a klystron comes from the fact that the voltage of the output cavity cannot be increased to large values (to extract considerable power from the electron beam) without reaching prohibitive power losses in the cavity.

It is an object of the present invention to provide means for extracting large amounts of energy from the electron beam of velocity modulated tubes.

Another object of the present invention is to provide a plurality of output cavities for a velocity modulated tube, which output cavities are coupled together.

A further object is to provide electromagnetic coupling for the output cavities of velocity modulated tubes.

A still further object is to provide thin metallic sleeves to support these output cavities.

These and other objects will become apparent from the following specification when taken in connection with the accompanying drawing in which:

Fig. 1 is a top axial cross-sectional view of one form of the invention;

Fig. 2 is a side view partly in section of the representation of Fig. l.

One method of increasing the energy given up to the electric field of a single cavity is to increase the voltage applied to the cavity, but as has been shown, power losses in the cavity will go up as the voltage squared rendering the cavity less efiicient, the greater the voltage. If the voltage is not increased in the single cavity, but if in accordance with this invention, another cavity is added having the same voltage, then the voltage given up to the electric field will be doubled and the power loss will be doubled instead of squared. The same principle applies to any number of cavities that may be used, and for a given voltage the greater the number of cavities used the greater will be the efficiency.

Referring to the Fig. 1, the entire structure of which is enclosed in an evacuated glass envelope (not shown),

supported by corresponding radial struts 13. and providing drift spaces 14. Output section 16 contains cavity 17. Coupling post 20 is contained both in cylinder 11 and output section 16. Collector-21 is contained in that part of coupling post 20 enclosed in cylinder 11. Cylindrical slot 22 is cut into the wall of output cavity 17 in such a manner that it encircles coupling post 20 at all points.

Referring to Fig. 2, more detail is shown of the construction of wire struts 13. Theyare fixedly secured to the walls of metallic sleeves 12, and cylinder 11, and in the instant embodiment are angularly spaced degrees;

Coupling post 20, slot 22, and output cavity 17 have the same appearance as in the view of Fig. 1.

In operation, metallic sleeves 12 are separated by small gaps which support the radio frequency field. The field acts on electrons from electron gun 10 in such a way as to velocity modulate the electron beam. The electrons become bunched due to the field contributed by the cavities along the first half of the tube and give up power to the radio frequency field along the second half of the tube. The tube operates in the mode in which the electric field extends in an axial direction in adjacent cavities. All other modes have a radial component of electric field and this radial component causes currents to flow in struts 13. Struts 13 are poor conductors and therefore all such modes are damped out.

For the purpose of velocity modulating the stream of electrons, it can be considered that the resonant cavities are bounded by sleeves 12; but the electric field created by sleeves 12 at any point in the area inclosed by cylinder 11 is the same throughout the whole cross sectional area of cylinder 11 taken at that point.

Energy is coupled from cylinder 11 to output cavity 17 by means of cylindrical slot 22. The dimensions of coupling post 20 are critical if a maximum amount of energy is to be coupled into output cavity 17. Formulas for finding the correct dimensions are Well known to those skilled in the art.

While a particular embodiment of this invention has been disclosed and described, it is to be understood that various changes and modifications may be made therein without departing from the spirit and scope thereof as set forth in the appended claims.

What is claimed is:

1. A velocity modulated beam type tube comprising, means for generating an electron beam, a hollow conductive shell defining an elongated chamber, a plurality of axially aligned annular sleeves positioned centrally within said chamber adapted to be traversed by said electron beam and serving to divide said chamber into a plurality of similar sections each resonant at the same frequency, struts extending radially from the interior surface of said shell and supporting said sleeves, and said struts being poor conductors whereby said struts act to damp all modes of oscillation in said cylinder which have a radial electric field component.

2. A velocity modulated beam type tube comprising, electron emitting means for forming an electron beam, a hollow conductive cylinder arranged coaxially with the beam path, means defining an output cavity, means including a collector electrode coupling said output cavity to said cylinder, a plurality of mutually spaced sleeves positioned in said cylinder along the beam path, supporting struts extending radially from said cylinder and supporting said sleeves, and said struts being poor conductors whereby modes of oscillation having a radial electric field component are suppressed in said cylinder.

3. A velocity modulated electron beam type tube comprising, means generating an electron beam, a hollow conductive cylinder, means :defining an output cavity, a conductivc .postterrninating :one end of said cylinder and coupling said cylinder to said output cavity, a plurality of mutually spaced sleeves arranged in succession within said cylinder along the path of-said electron'beannand struts having low conductivity extending radially from-said cylinder and supportingsaid sleeves.

-4. A velocity modulated beamtype tube comprising, an ,evacuatedenvelope, electron emitting means forforrning an electron beam, a hollow conductive cylinder arranged in said envelope coaxially with the beam path, one end .of said cylinder being terminated by a conductive plate having an aperture to admit said beam into :said cylinder means defining .an .output cavity, one wall .of said output cavity defining means terminating the other end of saidicylinder, said one wall having an aperture therein, a metallic post arranged coaxially with said beam path extending from said output cavity throughsaid last-mentioned aperture into said cylinder, a plurality of sleeves in said cylinder successively arranged along the beam path, each of said sleeves enclosing a drift space, radial struts extending from the interior wall of said cylinder and supporting said sleeves, said radial struts being poor conductors, whereby said struts act to damp all modes of oscillation in said cylinder which have a radial electric field component.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,026 Brown Apr. 14, 1942 2,403,795 Hahn July 9, 1946 2,409,608 Anderson Oct. 22, 1946 2,409,913 Tonks Oct. 22, 1946 2,455,094 Samuel Nov. 30, 1948 2,457,524 Bowen Dec. 28, 1948 2,464,349 Samuel Mar. 15, 1949 

